I find UI pretty buggy. You cant for example free balls that happened to be frozen behind buttons for debuffing boss without clicking these buttons. Skill buy button is always green even if you cannot afford that. No "buy max" buttons in Upgrades menu. Random ball fact stays on screen for too short time and like boss buttons really should be outside of main gameplay area.
In numbers only mode boss brick should be fully shown. Additional mode between OFF and LOW named BRICKS could be useful - shows only bricks without balls.
In non-UI related bugs, boss' crosshair freezes balls permanently (description says for 15 seconds).
This game dose not seem to be very much tested...